A corresponding shock absorber is known from DE 44 41 047 C1. Pressure-dependent damping valves for an exchange of fluid in the rebound and compression stage between two working spaces are provided on a piston which is guided axially within a cylinder tube. A pilot control means acts in such a way that a controllable pressure is built up in pilot control chambers. The pilot control pressure loads the valve plates of the damping valves into their closed position. By way of a bypass duct system, fluid is guided out of the working spaces into the pilot control chambers and the pressure is thus increased there. The pilot control pressure is regulated with the aid of a pilot control valve which can be set externally and is arranged in the bypass duct system. An elastic element forms the separating means between the pilot control chamber and the working space.
A further shock absorber which operates according to the same principle is known from DE 101 04 640 C1. In said document, the pilot control chambers are formed by way of pressure spaces. Said pressure spaces are formed by way of in each case one pressure space housing and one seal which lies movably on a damping valve. A pilot control valve controls the pressure in the pilot control chambers. An outlet of the pilot control valve opens into the working spaces.
U.S. Pat. No. 7,694,785 B2 discloses a similar application. The pressure in the pilot control chambers is likewise regulated via a pilot control valve. An outlet of the pilot control valve opens in each case into the respectively non-active pilot control chamber. This results, however, in an interaction between the function of the pilot control valve and the pressure in the non-active pilot control chamber, which interaction causes undesired side effects.
DE 101 26 555 C2 discloses a further arrangement, in which the pilot control valve likewise opens into the working spaces. A check valve prevents a direct inflow from the working spaces in the direction of the pilot control valve.
DE 100 20 778 B4 discloses a further shock absorber, in which, although it operates fundamentally according to the fundamental principle of DE 44 41 047 C1, a separate disk valve is provided here for each pilot control chamber for the regulation of the pilot control pressure. The two pilot control chambers are arranged in separate pilot control circuits and are therefore not connected to one another via a common fluidic connection. Furthermore, the damping valves are loaded into the closed position via a sliding element. A separate disk spring is in turn provided per sliding element, which disk spring loads the sliding element in the direction of the damping valve.
The pilot control pressures are changed at very short intervals. This is the case, above all, in shock absorbers of the type, in which the pilot control pressure is set in both pilot control chambers by way of merely one single pilot control valve. When driving over an uneven roadway (for example, cobblestones), the shock absorber can change between the rebound and the compression stage approximately between 10 and 20 times per second; the pilot control valve likewise correspondingly oscillates at a frequency of from approximately 10 to 20 Hz, in order to set the desired pilot control pressure for each stage. Said relatively high frequency oscillation generates instabilities in the form of high frequency harmonics in the profile of the damping force. This problem has not been noted up to now in the case of shock absorbers which have hydraulically separated pilot control circuits, as disclosed, for example, in DE 100 20 778 B4.